1. Field of the Invention
The present invention relates to acoustics and more particularly to transducers.
2. Brief Description of Prior Developments
The Tonpilz transducer has been the dominant technology for high-power underwater sound generation for many years. FIG. 1 is a schematic drawing of a typical transducer 1. A head-mass 3, piezoceramic stack 5 and a tail-mass 8 are bolted together with a tie rod 9 and nut 11. The other end of tie rod 9 is threaded and inserted into a tapped hole in head-mass 3.
The piezoceramic stack 5 consists of several annular rings 7 through which tie rod 9 passes. In FIG. 1 eight rings are shown, although numeral 7 is only shown for the uppermost three.
One such ring 7 is depicted in FIG. 2, which shows the central aperture 13 through which the tie rod passes. Also shown in FIGS. 1 and 2 are top electrode 15, consisting of metalization applied to the top surface of ring 7 and bottom electrode 17 consisting of similar metallization applied to the bottom surface of ring 7.
These electrodes are often somewhat smaller than the top and bottom surfaces of the piezoceramic ring 7 to prevent arcing when a high voltage is applied between electrodes 15 and 17.
In FIGS. 1 and 2, in each ring 7, an arrow 18 is shown to symbolically represent the piezoelectric polarization of the ring. By convention, when a positive voltage is applied between electrodes 15 and 17, the piezoceramic expands in thickness. Conversely, when a negative voltage is applied, the piezoceramic thickness decreases. If the voltage is an alternating voltage waveform such as sine wave, the piezoceramic will vibrate at the frequency of the waveform.
Referring to FIG. 1, when several rings are stacked up, all the top electrodes 15 are electrically connected together 19 forming a common external connection 21. Similarly, all bottom electrodes 17 are connected 23 to form a common external connection 25. It will be understood that a filled circle denotes an electrical connection, whereas a line crossing has no electrical connection. An open circle denotes an external connection.
Referring to FIG. 3, Tonpilz transducer 1 is connected by 21 and 25 to electrical matching elements 27 which are interposed between a power amplifier 29. Matching elements 27 may consist of a transformer 30, a capacitor 31 or an inductor 33 or a combination thereof, selected in accordance with the electrical properties of the transducer 1 and power amplifier 29 by techniques well know to those practiced in the art. These matching elements are used to optimize electrical efficiency. Electrical energy moves between the piezoelectric stack 5 and the matching elements 27 every half cycle of the applied voltage waveform.
Depending on the power levels to be achieved with the transducer, these matching elements, in particular inductors 33, may be physically large and require heavy gage wire to support the current requirements of the transducer. Often the required inductance is obtained using a magnetic core in inductor 33, leading to further size and weight to avoid saturation of the magnetic material. Once again, these techniques are well known to those skilled in the art.